1. Field of the Invention
The present invention relates to a magnetic recording and reproduction apparatus, and in particular to a magnetic recording and reproduction apparatus having a mechanism for moving a sub chassis relative to a main chassis.
2. Description of the Related Art
Recently, in the field of magnetic recording and reproduction apparatuses, the reduction of the number of components and the simplification of the structure has been actively pursued in addition to further reduction of size. Especially, a loading mechanism is very complicated and thus tends to have a larger number of components. Since the size and the number of components of the loading mechanism significantly influence the size and the cost of the video tape recorder itself, the development of the loading mechanism is very important.
A major part of the loading mechanism is a mechanism for driving a sub chassis. The development of this mechanism is very important.
Hereinafter, a conventional magnetic recording and reproduction apparatus will be described.
One known conventional magnetic recording and reproduction apparatus is described in Japanese Laid-Open Publication No. 11-328773. A loading mechanism of the magnetic recording and reproduction apparatus, especially a sub chassis driving mechanism, is shown in FIGS. 1, 3, and 24 through 30 of Japanese Laid-Open Publication No. 11-328773.
FIG. 1 of Japanese Laid-Open Publication No. 11-328773 is a plan view of a sub chassis driving mechanism of the magnetic recording and reproduction apparatus in a tape cassette mountable position (unloading mode). A sub chassis 3 is movable with respect to the main chassis 8. A sub chassis driving arm (not shown) on the main chassis 8 has a sub chassis driving pin 92 provided thereon, and the sub chassis driving pin 92 is in engagement with a groove 108 in the sub chassis 3.
FIG. 3 of Japanese Laid-Open Publication No. 11-328773 is a plan view of the mechanism shown in FIG. 1 (unloading mode) except that the sub chassis 3 is not shown. FIG. 3 is provided for illustrating a structure of the main chassis 8. A cam gear 66 is driven by a motor (not shown) mounted on the main chassis 8 to pivot about a support shaft 67. A sub chassis driving pin 75 is provided on a bottom surface of the cam gear 66. The sub chassis driving arm (represented by reference numeral 89 in FIG. 3) is engaged with the sub chassis driving pin 75. The engagement pivots the sub chassis driving arm 89 about a support shaft 90 as the cam gear 66 pivots. A sub chassis driving pin 92 is provided at a tip of the sub chassis driving arm 89.
With reference to FIGS. 24 through 30 of Japanese Laid-Open Publication No. 11-328773, an operation of the sub chassis driving arm 89 will be described.
FIG. 24 of Japanese Laid-Open Publication No. 11-328773 shows the positional relationship between the sub chassis driving arm 89 and the sub chassis driving pin 75 provided on the cam gear 66 (not shown in FIG. 24) when the magnetic recording and reproduction apparatus is in the unloading mode (tape cassette mountable position). The sub chassis driving pin 75 is engaged with a cam portion opening 91 including a first arc portion 121, a second arc portion 130, and a recessed portion 127. In this state, the sub chassis driving pin 75 is specifically engaged with the first arc portion 121.
From the state shown in FIG. 24, the cam gear pivots counterclockwise about the support shaft 67 to place the magnetic recording and reproduction apparatus into a state shown in FIG. 25. Since the sub chassis driving pin 75 is still in engagement with the first arc 121, the sub chassis driving arm 89 has not started pivoting about the support shaft 90 and the sub chassis engaged with the sub chassis driving pin 75 has not moved.
The cam gear further pivots counterclockwise about the support shaft 67 to place the magnetic recording and reproduction apparatus into a state shown in FIG. 26. In this state, the sub chassis driving pin 75 is released from the engagement with the first arc portion 121 and goes into engagement with the recessed portion 127. The sub chassis driving arm 89 starts pivoting about the support shaft 90, and the sub chassis engaged with the sub chassis driving pin 75 starts moving. After this, in accordance with the pivoting of the cam gear, the sub chassis driving arm 89 pivots counterclockwise about the support shaft 90, and the sub chassis also moves accordingly. When the sub chassis driving arm 89 arrives at a prescribed position, the sub chassis driving pin 75 is released from the engagement with the recessed portion 127 as shown in FIG. 27 of Japanese Laid-Open Publication No. 11-328773. In this state, the sub chassis driving pin 75 is in engagement with the second arc portion 130. Even though the cam gear pivots counterclockwise, the sub chassis driving arm 89 does not pivot and the sub chassis does not move. Only the sub chassis driving pin 75 moves in the second arc portion 130 as shown in FIGS. 28 through 30 of Japanese Laid-Open Publication No. 11-328773. As described above, the cam gear 66 is engaged with the sub chassis driving arm 89 having the cam portion opening 91 which has a size significantly larger than the diameter of the sub chassis driving pin 75. Thus, the sub chassis 3 is moved by the engagement of the cam portion opening 91 and the sub chassis driving pin 75 provided on the sub chassis driving arm 89.
In the above structure, only one side of the sub chassis driving arm 89 la engaged with the sub chassis driving pin 75, and the sub chassis driving pin 75 has a large separation from the far side of the cam portion opening 91 of the sub chassis driving arm 89. Accordingly, the position of the sub chassis driving arm 89 is not uniquely determined with respect to the sub chassis driving pin 75. Thus, the operation of the sub chassis driving arm 89 is unstable.
The conventional magnetic recording and reproduction apparatus described above has the following problems. As mentioned above, the position of the sub chassis driving arm 89 is not uniquely determined with respect to the sub chassis driving pin 75, and the operation of the sub chassis driving arm 89 is unstable. When an abnormal force is applied to the sub chassis driving arm 89, the sub chassis driving mechanism has a reliability problem. In addition, since the pivoting force of the cam gear 66 is first conveyed to the sub chassis driving arm 89 and then conveyed to the sub chassis 3, the number of components is increased. This hinders cost, size and weight reduction and also deteriorates the driving efficiency due to friction, increasing the load on the motor acting as a driving source. Since a plurality of components including the sub chassis driving arm 89 are located below the cam gear 66, the mechanism inevitably becomes thick. A large area in which the sub chassis driving arm 89 pivots also increases the size of the main chassis 8. These factors also hinder size and weight reduction.